The present invention relates to linear motors with multiple movers and in particular to a control system that provides a shared coordination subsystem greatly simplifying the programming and configuration of movers on the linear motor.
Linear motors take the principles of a standard rotary motor, for example, a synchronous permanent magnet motor, and adapt that for linear motion by effectively “unrolling” the rotor and stator. One type of linear motor provides a track having a set of individually energizable track coils separated along the length of the track. A mover is mechanically attached to move along the track and may include permanent magnets that interact with the coils that propel the mover allowing the mover to be moved and positioned at various locations on the track. By sequencing the coils, the mover may be passed from coil to coil along the track. By controlling the relative current flowing in coils adjacent to a mover, substantially continuous positioning of the mover between those coils may be obtained.
Despite the term “linear”, linear motors may include tracks that are not necessarily straight but that can curve, for example, in a loop, positioning the mover at various locations in the loop.
The interaction between the coils of the track and the mover is local so only coils adjacent to the magnets of the mover need be energized to control that mover. Accordingly it is possible to put multiple movers on a track and to control each mover independently.
A multi-mover, linear motor system can be advantageously applied to a number of industrial control problems, for example, moving a product of manufacture between various manufacturing stations. In this application, and unlike a conventional conveyor belt, the movers need not move in unison but can separate apart or bunch together as necessary, for example, forming small queues along the track to accommodate different processing speeds at various stations. A benefit of this capability is that it can greatly reduce the space between manufacturing stations and thus the size of the interconnected manufacturing system.
The ability to move a particular product on a mover without moving other products on a common track also allows higher-speed repositioning of product, allows the mover to participate in the processing of the product at each station, and allows cooperative participation by the movers in the manufacturing process by positioning different portions of a product on one mover with respect to other portions on a second mover.
Programming a multi-mover, linear motor system can be difficult. The movers can operate in close proximity requiring the programmer when repositioning a given mover to consider the positions of other movers with which it might collide. The conditions for collision can change significantly depending on the motion and inertial load of the various movers. Synchronizing motion of the movers can be extremely difficult resulting in a “caterpillar” effect wherein movers that should move simultaneously, begin and end their movements at different times, separating apart at the beginning of the move and then bunching up later in the move because of lags in the detection of the information from their immediate predecessor, much like a caterpillar stretching and contracting when it moves.
The challenge of programming a multi-mover, linear motor is exacerbated when they are used in an industrial control environment where control programs are constantly changing in response to new manufacturing problems and evolution of the manufacturing process.